The present invention relates to an image recording apparatus for recording image information, text information, etc., on a recording medium by using K (black), C (cyan), M (magenta), and Y (yellow) color toner sheets and a dummy sheet on which a recording medium is placed for use with the apparatus.
In a related image recording apparatus irradiates a recording medium fixed on a rotary drum with a laser beam, etc., from an optical head for recording an image. In this case, a toner sheet having a thermal-transferable toner layer formed on a substrate such as a transparent PET base, etc., and an image receiving sheet having an image receiving layer for receiving transferred toner are used for the recording medium. The toner sheet is heated in response to image data and the heated portion of the toner layer is transferred to the image receiving layer of the image receiving sheet, thereby recording an image on the image receiving sheet.
Specifically, a toner sheet comprising heat-molten or heat-adhesive color material layers (a light-heat conversion layer and a toner layer) formed on a substrate is used. The toner sheet and an image receiving sheet are superposed on each other at least at a recording position and the toner layer and the image receiving sheet are brought into intimate contact with each other. A latent image is formed on the toner layer by heating based on image data with a laser beam, etc., from the rear side of the toner sheet or the image receiving sheet, then the toner sheet and the image receiving sheet are peeled off, whereby an exposed portion of the toner layer is transferred to the image reception layer for transferring an image onto the image receiving sheet.
First, the related image recording apparatus will be discussed with reference to FIG. 9, which is a perspective view of the related image recording apparatus.
In FIG. 9, numeral 1 denotes an optical head being movable in a one-dimensional direction and having a plurality of laser beams for on/off-modulating the laser beams according to record data and applying the modulated laser beam. Numeral 2 denotes a rotary drum rotating at high speed with a recording medium placed thereon and numeral 3 denotes a recording medium for CTP (computer to plate), DDCP (direct digital color proofer), lith, or the like having a different structure in response to the use. Numeral 4 denotes a stage (or subscan stage) movable with the optical head 1 mounted thereon on a rail in parallel with the recording medium 3 on the rotary drum 2; while moving, the optical head 1 irradiates the recording medium 3 with a laser beam for recording an image. Such a movement corresponds to the subscanning direction at the time of image forming and the main scanning direction corresponds the rotation direction of the rotary drum 2.
Next, the structure of the recording medium 3 placed in the image recording apparatus will be discussed with reference to FIG. 10.
FIG. 10 is an illustration to show the structures of an image reception sheet 31 and a toner sheet 32 making up the recording medium 3 shown in FIG. 9. An actual recording process on the recording medium 3 is executed by a thermal transfer sheet such as the toner sheet 32 forming a part of a recording medium (for CTP, DDCP, lith, etc.,) as shown in FIG. 10. The toner sheet 32 is made up of a substrate 33, a light-heat conversion layer 34, and a toner layer 35 in order from the laser light application side. On the other hand, the image receiving sheet 31 is made up of an image receiving layer 36, a cushion layer 37, and a substrate 38 in order from the toner sheet 32 side. If the toner sheet 32 is superposed on the image receiving sheet 31 with the toner layer directed toward the image receiving sheet 31 side and laser light is applied, the toner layer portion to which the laser light is applied is heated and transferred to the light reception layer.
A material to allow laser light to transmit therethrough, such as a PET (polyethylene terephthalate) base, a TAC (cellulose triacetate) base, or a PEN (polyethylene naphthalate) base, is used as the substrate of the toner sheet 32 shown in FIG. 10. A substance for efficiently converting laser energy into heat, such as carbon, a black substance, an infrared absorption pigment, or a specific wavelength absorption matter, is used as the heat-light conversion layer. K, C, M, and Y color toner sheets are available as the toner layer; in addition, toner sheets of gold, silver, brown, gray, etc., may be used. The color toner sheets differ in heating and recording characteristics depending on the color.
The image receiving layer of the image receiving sheet 31 is adapted to receive transferred toner. The cushion layer serves as level difference absorption when toners are superposed at multiple stages. The structures also vary depending on the use; the used toner sheets and image receiving sheets are described in detail in Unexamined Japanese Patent Publications Nos. 4-26594A, 4-327982A, and 4-327983A according to the applications of the present applicant.
Next, a specific image recording procedure will be discussed with reference to FIGS. 11(a) to (f).
FlGS. 11(a) to (f) show recording process for executing a recording process on the image receiving sheet 31 shown in FIG. 10 for each of K, C, M, and Y. The recording process in each of the four colors K, C, M, and Y consists mainly of a step for executing laser recording according to color data and a step for peeling the toner sheet 32 from the image receiving sheet, 31 after recording.
A process for recording K color on a medium will be discussed.
At step (1), the image receiving sheet 31 is wrapped around the rotary drum, which is not shown for sake of clarity, but would be located under image receiving sheet 31 (FIG. 11(a)). Next, at step (2), to execute the K color recording process, a K color toner sheet 32 is put on the image receiving sheet 31 (FIG. 11(b)). Next, at step (3), they are laminated as required (FIG. 11(c)). Next, at step (4), the K color toner sheet side is irradiated with laser light for recording based on K color image, text data (FIG. 11(d)). Further, at step (5), the K color toner sheet 32 is peeled off the image receiving sheet 31 and the K color recording process is complete (FIG. 11(e)).
A process for recording C color on a medium like the K color recording process will be discussed.
At step (6), a C color toner sheet is put on the image receiving sheet 31. Next, at step (7), they are laminated as required. Next, at step (8), the, C color toner sheet side is irradiated with laser light for recording based on C color image, text data. Further, at step (9), the C color toner sheet is peeled off the image receiving sheet 31 and the C color recording process is complete.
A process for recording M color on a medium like the C color recording process will be discussed.
At step (10), an M color toner sheet is put on the image receiving sheet 31. Next, at step (11), they are laminated as required. Next, at step (12), the M color toner sheet side is irradiated with laser light for recording based on M color image, text data. Further, at step (13), the M color toner sheet is peeled off the image receiving sheet 31 and the M color recording process is complete.
A process for recording Y color on a medium like the M color recording process will be discussed.
At step (14), a Y color toner sheet is put on the image receiving sheet 31. Next, at step (15), they are laminated as required. Next, at step (16), the Y color toner sheet side is irradiated with laser light for recording based on Y color image, text data. Further, at step (17), the Y color toner sheet is peeled off the image receiving sheet 31 and the Y color recording process is complete.
Thus, at the last step (18), the four colors K, C, M, and Y may or may not overlap each other on the image receiving sheet 31, completing a necessary color image (FIG. 11(f)).
Thus, in the image recording apparatus, as shown in FIG. 9, the recording medium 3 comprising each toner sheet 32 using heat-molten, heat-adhesive, or sublimate toner superposed on the image receiving sheet 31 in intimate contact relation is pasted and fixed at the position determined by a registration on the surface of the rotary drum 2 and is irradiated with a laser beam, etc., from the optical head 1 for executing KCMY color image recording, etc. Since the rotary drum 2 rotates at fairly high speed during recording, air in the rotary drum 2 is sucked for lowering the pressure therein by an external air blower (or a vacuum pump, etc.,) as a suction source through a suction pipe and the recording medium 3 is vacuum-attracted through a large number of attracting holes made in the surface of the rotary drum 2 and an attraction groove for reliably holding and fixing the recording medium 3 so that the recording medium 3 does not float, shift, or curl up from the rotary drum 2.
FIG. 12 is a sectional view to show the principle of an attraction mechanism of the related rotary drum 2. The vacuum attraction mechanism is as follows: The rotation shaft of the rotary drum 2 is made hollow, is formed with a large number of rotation shaft holes 7, and is coupled to a suction pipe of the vacuum attraction mechanism such as an air blower 5 or a vacuum pump, and the blade of the air blower 5 is turned by a drive source such as a motor for sucking air in the rotary drum 2 through the rotation shaft holes 7 for reliably vacuum-attracting and fixing the recording medium 3 through attracting holes 21 of the rotary drum 2.
FIG. 13 is a fragmentary cutaway development view of the related rotary drum 2. In the figure, the outermost rectangle indicates that the rotary drum 2 is cut and developed along the axial direction. The rectangle inside the outermost rectangle is the recording medium 3 attracted onto the rotary drum 2. Each circle denotes an attracting hole 21. Here, the circles are drawn large for illustration to easily understand the placement relationship between the rotary drum 2 and the attracting holes 21 placed thereon. The actual size and number of the attracting holes 21 do not correspond to those shown in FIG. 13; the actual size is smaller than that in FIG. 13 and the actual number of the attracting holes 21 is greater than that in FIG. 13. An attraction groove 22 for strongly fixing the upstream leading end of the recording medium 3 is formed in the upper portion.
By the way, with the related image recording apparatus described, if a recording medium of a size smaller than the size matching the placement of the attracting holes 21 and the attraction groove 22 of the rotary drum 2 is used (see FIG. 14), attraction leakage occurs from some of the unclosed attracting holes 21 and the unclosed attraction groove 22 although an air blow having a large air flow quantity is used as the suction source. Thus, centrifugal force produced when the rotary drum 2 is rotated at high speed causes the recording medium 3 to be detached from the drum or makes insufficient intimate contact between the toner sheet 32 and the image receiving sheet 31, producing image unevenness. FIG. 15 is a graph to show change in vacuum pressure in the rotary drum 2 with respect to the number of unclosed attracting holes.
To solve this problem, the attracting holes 21 and the attraction groove 22 in the area other than the recording medium area of the rotary drum 2 can be previously covered with adhesive tape, etc. In this method, to cover the attracting holes, it is possible that tape and the recording medium do not overlap each other by finely changing the size of the recording medium 3 or adjusting the attachment position; however, the attraction groove 22 must be covered completely with the recording medium 3 or tape and it is difficult to attach the recording medium 3 without any level difference from the tape on the rotary drum 2. That is, the recording medium 3 and tape overlap each other or a clearance is created between the recording medium 3 and tape.
This covering method with tape requires that tape be stripped off and put or be changed in position each time the size of the recording medium 3 is changed; it is burdensome and also takes time. If the rotary drum 2 is on the outside of the apparatus, no trouble occurs, but if the rotary drum 2 is at the depth of the apparatus, the covering method with tape becomes complicated or cannot be handled by the user in some cases. When the adhesive of tape remains on the rotary drum 2, if the user does not notice it, the thickness direction of the recording medium 3 at the place changes and the focus with a laser spot is not obtained, thus image unevenness, etc., occurs and normal recording cannot be executed in some cases. Even if the user notices it, the remaining adhesive is not completely removed because it is hard to find visually, or if the rotary drum 2 is at the depth of the apparatus, the user is hard to reach the remaining adhesive and often cannot completely remove it. Thus, a fundamental solution cannot be provided by the method of covering with tape the attracting holes 21 and the attraction groove 22 in the area other than the recording medium 3 area of the rotary drum 2.
It is therefore an object of the present invention to provide an image recording apparatus, if a recording medium of a size other than the size matching placement of attraction groove and attracting holes of a rotary drum is used, for preventing the recording medium from being detached from the rotary drum or image unevenness from occurring due to insufficiently intimate contact between a toner sheet and an image receiving sheet making up the recording medium, and a dummy sheet on which a recording medium is placed for use with the image recording apparatus.
In order to achieve the above object, there is provided an image recording apparatus comprising: a rotary drum for attracting a recording medium to the surface thereof on which a plurality of through holes are formed, the rotary drum for attracting the recording medium via the plural holes by reducing pressure therein; a laser head for emitting a laser beam toward the recording medium on the rotary drum to record an image thereon; and a dummy sheet having an attracting area in which a plurality of through holes are formed, the area having a size substantially equal to the recording medium, the dummy sheet placed between the recording medium and the surface of the rotary drum such that the recording medium is placed on the attracting area and such that the plural through holes of the attracting area and the plural through holes of the rotary drum are superposed.
The dummy sheet may be formed into a size covering an outer periphery of the rotary drum.
The plural through holes of the dummy sheet and the rotary drum may include through holes formed into a slit shape.
According to the configuration, the dummy sheet is placed on the rotary drum and a recording medium is placed on the dummy sheet on the rotary drum, whereby the plural through holes of the rotary drum are closed almost completely. Therefore, even if an air blower having a small air flow quantity is used, the recording medium can be securely fixed to the rotary drum.
Therefore, if it is used a recording medium of a size other than the size matching the placement of the plural holes of the rotary drum, the recording medium is not detached from the rotary drum.
It may be configured that: the recording medium includes a toner sheet having a toner layer and an image receiving sheet having a smaller size than the toner sheet for receiving toner transferred by the laser beam, and the dummy sheet includes a spacer to be interposed between the surface thereof and the toner sheet.
It may be configured that: the thickness of the spacer is substantially equal to the thickness of the image receiving sheet.
It may be configured that: the spacer is provided on a circumferencial portion of the attracting area.
According to the configuration, the toner sheet is larger than the image receiving sheet, thus the extra portion does not overlap the image receiving sheet, producing a level difference. Then, to remove the level difference, the dummy sheet on which recording medium is placed is provided with the spacer for correcting the thickness of the extra portion of the toner sheet not overlapping the image receiving sheet (namely, correcting the level difference), whereby image unevenness is not caused by insufficiently intimate contact between the toner sheet and the image receiving sheet making up the recording medium or by distortion of deformation of the toner sheet.
It may be configured that: the image recording apparatus further comprises a plurality kinds of dummy sheets having a plurality sizes of attracting area corresponding to sizes of an image recording medium to be used, wherein a dummy sheet having a suitable size of the attracting area is selected and placed on the surface of the rotary drum before the recording medium is placed on the rotary drum.
Accordingly, recording media of various sizes can be reliably fixed to the rotary drum.
It may be configured that: the dummy sheet having an attracting area made of a porous material, the attracting area having a size substantially equal to the recording medium, the dummy sheet placed between the recording medium and the surface of the rotary drum such that the recording medium is placed on the attracting area.
According to the configuration, the dummy sheet need not be formed with through holes matching the placement of the plural holes of the rotary drum.